The sulfur content in iron ores and other materials commonly used in pig-iron production, i.e. coal and coke, have increased the costs of steel making. As a result, it is becoming increasingly desirable to desulfurize the pig-iron before the iron enters the basic oxygen furnace and/or steel making furnace. Over the years, a wide variety of materials and mixtures have been used to desulfurize the pig-iron. It has long been known that various calcium compounds are good desulfurization agents. It has also been known that magnesium, alone or in combination with various alkaline metal oxides, is also a good desulfurization agent. There have been several patents which disclose the use of calcium oxide and magnesium as the primary desulfurization agents. (See U.S. Pat. Nos. 4,765,830, to Skach; 4,708,737, to Skach; 4,705,561, to Green; 4,139,369, to Candler; 4,137,072, to Kawakami; and 3,998,625 to Koros). Furthermore, desulfurization agents disclosing the use of calcium carbide as the primary desulfurization agent have also been known and well documented. (See U.S. Pat. Nos. 3,598,573, to Freissmuth; 3,929,464, to Todd; and 4,395,282 to Braun).
Recently, the use of a calcium compound and magnesium, in combination with a gas-producing compound, has been used to increase the amount of sulfur removal. It has been found that the gas-producing compound releases a gas upon contact with the molten pig-iron to create a turbulent environment within the molten pig-iron. The released gas primarily breaks down agglomerations of the desulfurization agent and disperses the desulfurization agent throughout the molten pig-iron. The gas-producing agent is typically a hydrocarbon, carbonate or alcohol which has a tendency to release various amounts of gas upon contact with the molten pig-iron. Use of these various gas-producing agents is well documented. (See U.S. Pat. Nos. 3,876,421, to Takmura; 4,078,915, to Meichsner; 4,194,902, to Gmohling; 4,266,969, to Koros; 4,315,773, to Freissmuth; 4,345,940, to Koros; 4,705,561, to Green; 4,592,767, to Reliermeyer; 4,764,211, to Meichsner; 4,832,739, to Meichsner; and 5,021,086, to Luydkx).
Desulfurization agents may also contain various slag-forming agents. Previously, the importance of the slagging agent has been passed over for more immediate concerns about the economics of using various ingredients of the desulfurization agent. Although it is important to use the proper desulfurization components to react with the sulfur in the pig-iron and separate the sulfur from the pig-iron, the composition of the slag is very important to retain the removed sulfur within the slag and not allow the sulfur to re-enter the molten pig-iron.
Various slagging agents have been used for various purposes. In U.S. Pat. No. 4,315,773 a desulfurization agent comprising calcium carbide, a gas-involving compound, and fluorspar is disclosed. Fluorspar is used to modify the properties of the slag to prevent carbon dust production from igniting during the desulfurization.
In U.S. Pat. No. 5,021,086, fluorspars are used to modify the characteristics of the slag increasing the fluidity of the slag during the desulfurization process.
At the present time, concerns of balancing the proper use of various desulfurization agents to remove sulfur from the pig-iron with the slag forming agents, which entraps the removed sulfur and prevents the sulfur from re-entering the pig-iron, have not been previously disclosed in the art. As a result of the inadequate attention to the slag characteristics during the desulfurization process, there is now a demand for better slagging agents to ensure easy removal of the slag and to ensure proper entrapment of the sulfur within the slag to optimize the sulfur removal from the pig-iron.